Non-invasive Method And Model Study For The Measurement Of Blood Oxygen Saturation Rate In Wide Range

The arterial blood oxygen saturation rate is defined as the percentage of the concentration of oxyhemoglobin, or HbO₂, with the total hemoglobin concentration. In clinic, the measurement of blood oxygen saturation rate has an important significance. At present, the conventional method is the two wavelengths linear method, which can measure the blood oxygen saturation rate correctly within the range of 70% to 100%. But in the wider range, there are two problems. One is that, in the low oxygen range of 35% to 70%, the error measured by liner method is larger. The other is that the absorption coefficient of oxyhemoglobin and deoxyhemoglobin, or Hb to red light and the near infrared measured by biochemical method is different from that measured by pulse two wavelengths. So we do some related work as follows.Based on the conventional model and method for the non-invasive measurement of blood oxygen saturation rate, the improved model is introduced, which takes the influences due to the other material except HbO₂ and Hb in arterial blood and the material such as surrounding tissues, venous blood, muscles and so on into consideration. Besides, the non-linear method is derived and the concept of equivalent absorption coefficient is introduced and explains the contradiction due to the conventional linear method.A non-invasive pulse oxymeter in wide range is designed using the CAN bus communication and fast digital signal processing. And the components and functions of the oxymeter are introduced in detail. An Index 2 blood oxygen saturation rate simulator produced by FLUKE company is used to calibrate the pulse oxymeter we designed. The experiments indicate that the oxygen saturation rate can be correctly measured by the pulse oximeter we designed in the wide range of 35% to 100% within±3% accuracy.In conclusion, the improved model explains the difference between the absorption coefficient of oxyhemoglobin and deoxyhemoglobin measured by biochemical method and the equivalent absorption coefficient. The improved method can measure the oxygen saturation rate correctly in the wide range of 35% to 100%, and reduce the error, which has great academic and practical significance. And part of the research results has been used to measure the cosmonauts' circadian signals and get a good effect.